Short Communications ▶ Liquid chromatography tandem mass spectrometry method for determination of N-acetylcysteine in human plasma using an isotope-labeled internal standard (pages 427–431) Chuan Lu, Gangyi Liu, Jingying Jia, Yuzhou Gui, Yanmei Liu, Mengqi Zhang, Yun Liu, Shuijun Li and Chen Yu Abstract ▶ Usefulness of the simultaneous determination of serum levels of theophylline and its metabo..